The present invention relates to a display device with scale, pointer, stepping motor, gearing and control means in which a plurality of revolutions of the stepping motor corresponds to the entire display range, and the control means contains a step counter with reversibly unambiguous association of number of steps and display value.
The proper association of display value and number of steps is checked upon the manufacture of the display device or upon its initial placing in operation and, if necessary, adjusted. This adjustment is not sufficient for dependable operation since the correct association can be interfered with by interruption of the source of power or by the effect of electromagnetic waves.
A method has already been proposed (German OS 39 21 462) for a stepping motor having multiple windings in which the voltage induced by a movement of the stepping motor in a winding not required at the time for the drive is evaluated. The evaluation is effected in the manner that each time that the stepping motor is placed in operation, a test program is first performed in which the stepping motor is moved further in a predetermined direction until the pointer comes to a stop at the end of the scale, this being noted by the absence of an induced voltage when the stepping motor is stopped. The test program is thus completed and the step counter can be set to the corresponding value. The display device is now readjusted and is ready for operation.
By this method, automatic adjustment can be effected upon each connection and/or disconnection of the display device. However, this cannot be employed for all cases of use since the association of number of steps and display value may be disturbed also during operation, for instance by electromagnetic radiation acting temporarily from the outside on the counter or by strong mechanical vibrations.